Grinding mill lining and control of the wear thereof



1965 R. J. RUSSELL ETAL 3,

GRINDING MILL LINING AND CONTROL OF THE WEAR THEREOF Filed Sept. 1'7, 1962 2 Sheets-Sheet 1 F/Cil F l G. 3

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BZ INVENTOR (0 75 ROBERT J. RUSSELL HARLO we HARD/NGE 5 B FIG. 4

ATTORNEY Oct. 12, 1965 R. J. RUSSELL ETAL GRINDING MILL LINING AND CONTROL OF THE WEAR THEREOF 2 Sheets-Sheet 2 Filed S'epb. 1'7, 1962 INVENTOR ROBERTJ. RUSSELL HARLOWE HAROINGE- ATTORNEY United States Patent GRINDING MILL LINING AND CONTROL OF THE WEAR THEREOF Robert J. Russell and Harlowe Hardinge, York, Pa., assignors, by mesne assignments, to Koppers Company, Inc., Pittsburgh, Pa., a corporation of Delaware Filed Sept. 17, 1962, Ser. No. 224,075 12 Claims. (Cl. 241-26) This invention pertains to grinding mills and, more particularly, to the lining of various kinds of grinding mills, the invention principally being concerned with means and arrangements, as well as a method, for controlling the wear of the mill lining, especially to lessen the cost of upkeep thereof, and also lengthen the life of the lining means of the mill.

In general, the invention pertains to lining and material lifting means in various kinds of grinding mills, such as, for example, ball mills, pebble mills, rod mills, and, more particularly, grinding mills arranged to comminute friable material autogenously by using various sizes of the material as its own grinding media while being tumbled within the mill.

Ball, pebble and rod mills are of the rotating type, and the length thereof in an axial direction is generally either equal to or substantially greater than the diameter of the mill. The term pebble mill also includes that type of autogenous tumbling mill wherein selected, larger fragments or pebbles are used as grinding media to reduce the so-called feed size which is considerably smaller. For example, if a mesh feed is to be ground in such a mill, then pebbles of 1 to 3" would be selected, or if, for example, the feed size is of the order of A to 1" maximum size, then 5" to 7" size pebbles or fragments of the same material would be employed. The size ranges selected here are examples only and are subject to wide variation, depending upon conditions and the material being ground. In contrast to this, however, in an autogenous grinding mill handling so-called run-ofmine material which is usually the direct product of a primary crusher and consists of all sizes, large, medium and small, the most effective type of mill is that in which the axial length of the interior-space within the mill is substantially less than the diameter thereof. Essentially, this is for purposes of effecting a thorough intermixing action and a normally higher lifting and cascading effect of the material within the mill of the autogenous type than occurs within mills of the aforementioned types. Greater impact and mixing of the falling material is achieved for purposes of simultaneously reducing all size ranges of the material within the autogenous mill.

In all mills of these various types, the construction usually comprises a metallic shell of suitable thickness to form a rigid housing, but the nature of the metallic shell, even though of appreciable thickness, is such that the shell per se is not capable of sustaining the abrasion and impact normally occurring Within the mill as the result of the material tumbling therein, and particularly if the active grinding media comprises metallic balls, rods, or tubes, or non-metallic pebbles, or the like, formed from flint and other hard substances. Depending, too, upon the nature of the raw material being handled in an autogenous grinding mill, it frequently occurs that the material itself is relatively hard and thereby subjects the inner surface of the mill to substantial abrasion and impact.

In order to afford the mill a reasonable industrial life, it has long been customary to provide the shells of such mills with interior liner plates, sections, or segments, which usually are detachably connected against the inner surface of the shell of the mill, including the peripheral portion, as well as the ends thereof. Such removable liner elements are secured in place either by appropriate bolts extending through the shell of the mill, or by wedge bars disposed within appropriate spaces between the edges of adjacent lining elements, the wedge bars being attached to the shell by suitable bolts. Various kinds of arrangements of this type have been used for many years.

It also has been customary for a long period of time to utilize the wedge bars, both on the peripheral portions, as well as the ends of mills of this type, for the double function of not only connecting the liner elements to the shell of the mill, but also acting as lifting means. For example, in ball, pebble and rod mills wherein the length thereof usually is greater than the diameter, the interior of the mill is provided with substantially parallel lifter bars projecting radially toward the axis of the mill and parallel thereto, said lifter bars being spaced circumferentially around the interior of the peripheral portion of the mill. As the mill rotates, the lifter bars comprise projections which are engaged by the material being tumbled within the mill, as well as the grinding means or media when employed, and tend to hold segments of the material within the mill substantially stationary relative to the interior of the mill until the material reaches a certain height within the mill when gravity overcomes the holding effect of the lifter means and permits the material to tumble or cascade over itself within the mill, simultaneously effecting grinding action.

The ends of the mill, particularly of the type for reducing coarse feed size ranges, are provided with radially extending lifter bars which, in addition to their lifting function, likewise frequently serve to wedge or otherwise secure the liner sections or segments upon the ends in their operative position so that, at all times, all portions of the shell of the mill are protected against abrasion and wear.

Heretofore, it has been customary to use wedge bars, both those connected to the peripheral surface of the mills, as well as the ends thereof, which are of a uniform height or radial dimension, for example, in a radial direction inwardly toward the axis from the inner surface of the liner elements. It is obvious that as the mills rotate, such wedge and lifter bars will be subjected to substantial abrasion and impact, substantially uniformly, whereby all of such bars t end to wear away not only at the edges, thereof, but generally along the outermost surfaces, whereby the radial dimension of the bars gradually is reduced until their lifting ability has diminished to the point where they must be replaced for further eflicient operation of the mill.

When these lifter bars are in relatively new condition,

and therefore are of a reasonable height, depending upon the lifting requirements required by the mill, they tend to minimize wear upon the liner elements extending between the lifter bars. However, as the radial height of these lifter bars is reduced through wear, they offer less protection for the liner elements and, as a result, the liner elements also become Worn and, depending upon the original thickness thereof, eventually will require replacement, but usually not as often as replacement of the lifter bars is required.

It is the principal object of the present invention to provide within grinding mills various types of liner and contour-forming means which are so arranged that thegrinding effect, as well as the wear rate of the interior liner and contour-forming means, will be substantially constant over much longer periods of time than now is possible in mills of this type utilizing conventional types of lining means and lifter bars, whereby the periods within which the mill is out of use, as the result of the necessity of replacing the liner means and/ or lifter bars, is reduced to a minimum.

Another object of the present invention is to provide rotatable tumbling mills of the type referred to with several sizes of lifter bars respectively of medium and high radial dimensions or heights, for example, these radial bars of different heights being arranged successively around the periphery of the mill, as well as on the ends thereof if lifter bars are utilized on the ends of the mill, whereby as the lifter bars progressively wear and the radial dimension or heights thereof gradually are reduced so that the intermediate bars become low and the high bars become intermediate in height, it will only be necessary to replace the worn low bars with relatively high bars, thereby resulting in a minimum of waste scrap being expended in the form of such worn lifter bars, and, in addition, the replacement time is substantially reduced, but, more importantly, during the operation of the mill, the relative dimensions of the lifter bars with respect to the liner elements therebetween are maintained much more constant with respect to each other than occurs in mills where the lifter bars are all substantially of the same height.

It is a further object of the invention to even out the wear of the liner elements between the lifter bars by the use of alternately intermediate or medium height lifter bars and high lifter bars due to the fact that, with respect to the direction of rotation of the mill, the maximum wear upon the liner elements is farther from the lifter bars in a trailing direction with respect to the high bars than the lower height of lifter bars, whereby when the intermediate height bars become worn to replacement size, the wear upon the trailing liner element is close to the bar, while after the worn bar is replaced with a so-called high lifter bar, the wear upon this same trailing liner element will occur much farther from said bar than when the worn bar of original intermediate height was being used, and thus there gradually is an overall evening out of the wear upon the liner elements between the lifter bars, particularly in the peripheral sections of the mill.

A further object of the invention is to minimize wear upon the lining means of the mill by reducing the sliding effect due to the provision of the aforementioned types of successively different heights of lifter bars, which result at all times in at least alternate lifter bars being relatively high in a radial direction, as compared with all of the lifter bars wearing simultaneously to substantially even radial heights, as is the common experience in conventional mills of this type.

Still another object of the invention is to enhance the efficiency, particularly of autogenous grinding mills, wherein maintenance of substantially constant interior contour within the mill is a prime requisite to the achieving of maximum grinding efficiency due to the fact that in mills of this type, the lifting action of various size ranges is a very important factor among all of the various factors which have to be coordinated in order to achieve maximum grindiing efficiency in this type of mill, and the maintenance of these factors substantially constant, in relation to the various components comprising the contour, eliminates one of the principal variables in autogenous grinding mills in which the lifter bars are substantially all of the same height and uniformly wear during operation of the mill so as gradually to decrease the lifting effect thereof.

Another object is to test different liner contours to obtain optimum operation, and then employ means and methods to maintain essentially a constant contour and grinding efficiency, taking into consideration progressive wear.

Details of the foregoing objects and of the invention, as well as other objects thereof, are set forth in the following specification and illustrated in the accompanying drawings comprising a part thereof.

In the drawings:

FIG. 1 is a side elevation, partly broken away, of an exemplary autogenous grinding mill in which the ends thereof are of the conical type and within which mill the liner means and lifter bars are arranged in accordance with the present invention.

FIG. 2 is view similar to FIG. 1, but illustrating another embodiment of autogenous grinding mill in which the ends are substantially parallel, but within which mill the lining and lifter bars are arranged in accordance with the present invention.

FIG. 3 is a side elevation, partly broken away, of an elongated type of mill, such as commonly found in ball, pebble and rod mills, said mill being adapted for continuous feed and discharge of mineral products and the interior of the mill being provided with lining and lifter means arranged in accordance with the present invention.

FIG. 4 is a transverse sectional view of the mill shown in FIG. 3, as seen on the line 44 of said figure.

FIG. 5 is a vertical sectional view through the mill illustrated in FIG. 1, and illustrating in an exemplary manner the disposition of material within the mill while undergoing reduction so as to show the cascading and tumbling action to which the contents of the mill are subjected, a similar effect also occurring in the mill shown in FIG. 2.

FIGS. 6, 7 and 8 respectively are progressive views of similar transverse segmental sections of peripheral portions of the various mills illustrated in FIGS. 1-3, and in which views the liner elements and transverse lifter bars are shown progressively in relatively new, worn, and partially replaced or restored conditions, in accordance with the principles of the present invention.

FIGS. 9, 10 and 11 respectively are sectional views similar to FIG. 6 and individually illustrating different shapes and kinds of liner elements and transverse lifter bars employing the principles of the present invention.

FIG. 12 is a fragmentary sectional view showing details of a preferred type of lifter bar mounting structure.

Inasmuch as the present invention is particularly of importance to autogenous grinding mill for purposes of maintaining substantially constant contour shape on the interior of the mill so as to afford substantially constant lifting effects, the majority of the views shown in the drawings illustrate various types of autogenous mills in which the axial length of the interior of the mill particularly is substantially less than the diameter of the interior of the mill within which the grinding takes place autogenously. Such so-called narrow mills are highly effective to accomplish autogenous grinding of run-of-mine material and operation of the mill without requiring any substantial adjustment over long periods of time to produce optimum grinding efficiency is possible, once the optimum grinding conditions have been established. Although less efficient, a mill with a relatively long drum, compared to the diameter, may also be employed for grinding run-of-mine material autogenously.

Much of the efficiency of mills of this type resides in the fact that means are provided therein for effecting transverse movement of all size ranges of the material within the mill, in an axial direction, while the mill is rotating, particularly for purposes of constantly moving the coarser size ranges of material away from the screening means which are usually disposed adjacent the exit end of the mill and through which principally relatively fine and intermediate size ranges of material are discharged for passage through the exit of the mill. For a more complete discussion of the details and advantages of the construction and operation of autogenous mills of the type shown in FIGS. 1 and 2 than is given hereinafter, attention is directed to co-pending application Serial No. 822,612, by Harlowe Hardinge, filed June 24, 1959, now Patent No. 3,078,049.

Autogenous grinding, as the name implies, comprises using the material itself which is undergoing reduction as its own grinding media. Autogenous grinding particularly is effective for purposes of handling run-of-mine material in which substantial ranges of relatively coarse, medium and fine sizes of material are included. The larger size ranges serve somewhat as pebbles or grinding media to further reduce the intermediate and finer size ranges, but, in turn, the larger or coarser size ranges likewise gradually are reduced in size. The use of metal balls or like media intermixed with the charge is also contemplated under certain conditions. Depending particularly upon the type of material being treated, and especially considering the hardness thereof, the lifting effect to which the material is subjected is of importance in the operation of an autogenous grinding mill. Hence, the temporary holding of the bulk of the material between the ends of the socalled narrow mills illustrated in FIGS. 1 and 2, coupled with the eifect afforded by appropriate transverse lifter bars, usually will result in the material being elevated to a rather substantial height within the mill, depending also upon the speed of rotation of the mill, before the material tumbles or cascades down the slope afforded by the bulk of the material being tumbled within the mill, as illustrated in exemplary manner in FIG. 5 of the drawings.

The provision of various means within the interior of the mill which are engaged by the material as it falls or tumbles causes transverse movement of the material, as well as such transverse movement of various size ranges of the material within the bulk thereof, incident to being tumbled, whereby not only is additional grinding effected in this manner, but screening means, when employed, such as a grate, provided in the exit end of the mill is caused to function effectively, particularly by the progressive clearing from the inner surface thereof of especially the coarser particles of material which have not yet been reduced suifici-ently in size to pass through the openings of the screening means. All of such grinding action, however, subjects the lining elements and lifter bars on both the peripheral, as well as the end portions, of the mill to substantial impact and abrasion, and this occurs not only in autogenous grinding mills, but in other types of rotatable tumbling mills, as well, as illustrated in exemplary manner in FIGS. 3 and 4, and to which the present invention also pertains.

Referring to the exemplary autogenous grinding mill in FIG. 1, the peripheral portion of the shell extends between the conical inlet end 12 and the conical discharge end 14. Suitable hollow trunnions 16 and 18 support the mill rotatably in conventional bearings, not shown, and respectively serve as inlet and exit means for the mill. A stationary feed chute 20 extends through the entrance trunnion 16, while an exitcone 22 extends through the exit trunnion 18. Appropriate drive means, not shown, serve to rotate the mill at required speeds, as determined for optimum grinding efliciency of the mill.

The interior of the mill, adjacent the conical end 12, is provided with liner segments 24 of hard, wear-resistant material, the peripheral edges of such liner segments preferably being shaped or slightly spaced so as to receive therebetween radial wedge and lifter bars 26 and 28, respectively of diiferent heights. The bars 26 are considered, for example, to be of intermediate or medium height, while the bars 28 are considered to be high bars, for purposes of describing the present invention. Conventional bolts secure the lifter bars and liner segments to the end 12 of the mill shell.

The peripheral portion 10 of the mill shell, likewise, is provided with curved liner segments 30 and 32, which have inner surfaces sloping toward each other toward the center of the mill, for purposes of eflecting lateral movement of material which engages the same, in an axial direction within the mill. Different heights of transverse wedge and lifter bars 34 and 36, respectively of medium height and high bars extend between the edges of the liner segments 30 and 32 and are secured to the mill shell by conventional T-shaped heads or wedge bolts 38, shown, for example, in FIGS. 1 and 12. The circumferential spacing of the medium and high transverse lifter bars 34 and 36 is shown in exemplary manner in FIG. 5, the curved shape of liner segments 32 also being illustrated therein, and it will be understood that segments 30 are similarly curved. The alternate arrangement of relatively high and low transverse lifter bars likewise is shown advantageously in FIG. 5.

FIG. 5 primarily is an interior view of the exit end 14 of the mill and said exit end includes screening means which preferably comprise segmental grate sections 40. The ends of the sections of the grate 40 are preferably spaced circumferentially to receive therebetween the radial lifter bar sections 42 and 44, which respectively are of medium height and high bars, as best shown in FIG. 1, and secure the screening means to the exit end of the mill. As with respect to the other lifter bars, the grate sections are secured by appropriate bolts 46 to the shell end 14.

An annular discharge space 48 of appreciable depth in axial direction is formed between the grate 40 and the end 14 of the mill shell for purposes of receiving the relatively fine and medium size ranges of material discharged through the openings in the screening means comprising said grate sections. Also disposed within the space 48 are radially extending and circumferentially spaced blades 50 comprising lifters, which carry the material upward until gravity permits the same to fall against the conical end 52 of the mill which causes it to be discharged through the exit cone 22 and deflects the falling material axially outward into cone 22 for discharge from the mill.

Additional means also are provided within the mill shown in FIGS. 1 and 5 which are engaged by the falling and tumbling material and comprise annular deflecting rings 54 and 56, these serving to effect desired transverse movement of various size ranges of the material within the mill in an axial direction. Further, the conical arrangement of the liner segments 24 and grate sections 40, as well as the radial bars extending thereacross, also comprise deflecting means which effect transverse movement of the material, whereby it will be seen that a very substantial amount of abrasion and impact is imposed upon the liner segments and the lifter bars, both radial and transverse, as a result of the autogenous grinding of the material being treated within this type of mill. However, due to the provision of the alternate exemplary medium height and high lifter bars of both the radial and transverse type, as illustrated with respect to the radial in FIG. 1 and transverse in FIG. 5, it will be seen that a substantially constant interior contour of the mill is achieved, as can best be appreciated by reference to FIGS. 6, 7 and 8, for the following reasons.

In FIG. 6, an exemplary segmental section of the peripheral portion shown in FIGS. 1 and S is illustrated on a larger scale than in said figure. The representation in FIG. 6 simulates an exemplary condition of the mill when the peripheral liner 32 and the medium height and high lifter bars 34 and 36 are substantially in new condition. After a period of wear, the condition of this same exemplary contour shape becomes as illustrated in FIG. 7, in which the initially high lifter bars now are indicated 36, whereas the initially medium height bars have been indicated 34. It is apparent therefore that the worn high bars 36 are substantially, for example, the same height as the new medium height bar 34 shown in FIG. 6, while the worn medium height lifter bar 34' of FIG. 7 clearly is ready for replacement, because its lifting ability in this condition is practically nil.

The Wear pattern imposed upon the curved liner segments 3t] and 32, of which only the segments 32 are shown in FIGS. 68, also is of interest. Referring to FIG. 7 particularly, it will be seen that because of the greater height of bar 36 than bar 34', the wear imposed upon the segment 32 which trails the left-hand lifter bar 36' occurs in substantially spaced relationship, at 58, for example, and closer to the worn medium height bar 34' than the left-hand worn high bar 36'. However, the segment 32 which trails the intermediate worn medium bar 34' has a wear area 60, which is closer to bar 34' than the trailing initially high bar 36'.

Considering now the peripheral liner conditions shown in FIG. 8, wherein the worn initially medium height bar 34- has been replaced with a new high lifter bar 36, while the worn initially high lifter bars 36' remain in the mill 80 as now to serve as medium height bars, the wear effect upon the liner segments 32 now will result in a new wear area 62, shown in broken lines in FIG. 8 immediately trailing the left-hand bar 36', due to the lower height of the bar 36 than that which it had that produced the wear area 58, which will become more evident as bar 36' wears down to approximate that of bar 34 before being replaced later by a high bar 36. Thus, it will be seen that the wear areas of the liner segments 32 between successive lifter bars, under the conditions explained above, will succeed each other, rather than be coincident and thereby extend the life of the liner segments between the lifter bars to a far greater extent than would be possible under current conditions where the lifter bars are all of substantially the same height, all wear down substantially at even rates, and all are replaced simultaneously, considered particularly in the light of the fact that effective lifting capacities are meanwhile maintained within the mill as a result of the replacing of alternate worn initially medium height lifter bars 34' by new high lifter bars 36.

It will be understood, of course, that, with respect to the arrangement shown in FIG. 8, and assuming that there is still adequate thickness of the liner segments 30 and 32 to warrant leaving the same in the mill, the next replacement step would be to replace the now completely Worn out initially high lifter bars 36' with new high lifter bars 36, it being understood that at this time the new high lifter bars shown in FIG. 8 will have become Worn to substantially half their present height so that it then will constitute a lifter bar of medium height, such as initial bar 34 shown in FIG. 6. As a result of this, the cycle now has completely repeated itself, and it will be seen that the alternate medium height and high lifter bars progressively change position around the mill with each replacement. After the initially medium high lifter bars 34 are worn out and have been replaced, the only sized bar which need be obtained thereon for replacement are the high lifter bars 36. A similar wear and replacement sequence as described for the mill periphery occurs and is applicable to both mill ends, including the bars holding the mill grate.

In order that the adaptability of the present invention to other types of both autogenous and non-autogenous grinding and tumbling mills may be appreciated, examples of these respectively are illustrated in FIGS. 2 and 3. Functionally, the mill shown in FIG. 2 is an autogenous mill, and aside from a few details which are peculiar to the autogenous grinding function per se, the mill shown in FIG. 2 is equivalent to that shown in FIG. 1, as far as the present invention is concerned, and comparable elements of the mill shown in FIG. 2 have been given the same reference characters as those in FIG. 1, except that a prime has been added to each of the numerals in FIG. 2 where the numerals designate corresponding or equivalent elements.

The principal difference between the mill shown in FIG. 2 over that shown in FIG. 1 is in regard to the extent of the grate 40', which, as will be seen by comparing the same with the grate 40 in FIG. 1, is spaced at its outer periphery from the interior of the peripheral portion 10' of the mill. Also, the ends 12' and 14 are substantially parallel to each other, and said mill also has an annular expanded zone 66, within which material undergoing reduction can expand during the grinding operation of the mill, and thereby, under certain circumstances, enhance the autogenous grinding of the material.

As in regard to the mill shown in FIG. 1, the lifter bars and the liner sections of the mill in FIG. 2 are subjected to extensive impact and abrasion, but, by employing the invention described in detail relative to the mill shown in FIGS. 1 and 5 with respect to the use of alternate lifter bars of different heights, the contour of the interior of the mill shown in FIG. 2 remains substantially constant, for the same reasons as explained above with regard to the mill specifically shown in FIGS. 1 and 5. There also is an additional annular deflecting ring 68 in the mill shown in FIG. 2, which is operable to effect a lateral movement of the material in the mill, and also serves to protect the screening diaphragm comprising grate sections 40' from excessive abrasion through contact by the material moving within the grinding zone of the mill.

The elongated type mill shown in FIG. 3 is substantially more simple than the autogenous grinding mill shown respectively in FIGS. 1 and 5 and FIG. 2.. The mill 70 may, for example, be a rod, ball or pebble mill, or the like, including that type of autogenous mill utilizing relatively coarse pieces of the same material as that fed in finer unfinished sizes thereto. While not generally as efiicient or as practical as the type of mills shown in FIGS. 1 and 2, this mill shape can also be employed to handle run-of-mine material the same as that type illustrated in FIGS. 1 and 2, and this invention contemplates the use of the same in this manner when considered advisable to do so. The length of the mill is usually substantially greater than the diameter thereof. The mill 70 is rotatably supported upon trunnions 72 and 74 at opposite ends thereof, these respectively being entrance and exit means as well and, in this particular exemplary illustration of the mill, a grate 76 is provided adjacent the exit end of the mill to size the material being discharged therefrom.

As far as the present invention is concerned with respect to the embodiment of mill shown in FIG. 3, the principal items of interest comprise the peripheral liner segments 78, which extend between the opposite ends of the mill and the alternate longitudinally extending high lifter bars 80 and medium height lifter bars 82. If desired, the ends of the mill 70 also may be provided alternately with high and medium height lifter bars, Further, the longitudinally extending lifter bars 80 and 82 may be employed to retain, in operative position against the mill 70, the peripheral liner segments 78. Also, it is the longitudinally extending lifter bars 80 and 82 which will be subjected to the primary impact and abrasion type of wear, as distinguished from any other lifter bars within the mill, such as those possibly on the ends thereof, in addition, of course, to the peripheral liner segments 78, which, likewise, are subjected to substantial impact and abrasion type of wear.

The lifter bars 34 and 36 shown in transverse section in FIGS. 58 preferably are each of a composite or twopart construction, exemplary details of which are shown in FIG. 12 on a larger scale than in said preceding figures. In regard to both heights of the exemplary bars 34 and 36, the upper or wear portions are separable from the wedge bar or root portions 83. The opposite sides of the wedge bars 83 respectively engage adjacent and complementary edges of the liner plate segments 30 and 32. Preferably, wedge bolts 38 extend through both the upper portions 34 and 36 and wedge bars 83 of each composite lifter bar, as well as through the shell plate 10, to secure all of said items assembled in operative position.

This composite lifter bar construction is of particular advantage relative to the present invention in that it minimizes waste when discarding worn upper portions of the lifter bars since the wedge bars 83 usually are in such condition that the new replacement upper portions of the lifter bars will fit the upper surfaces of the wedge bars 83. Another advantage lies in the fact that by letting the wedge 'bars 83 remain in place while replacing the worn upper portions 34 and 36, the liner plate segments are not disturbed, whereby overall elapsed time for such replacement is minimized. This aspect of the invention also is applicable to the embodiments shown in all other figures of the drawings, if desired.

By employing the concept of the invention explained in detail above, particularly with regard to the embodiment of mill shown in FIGS. 1 and 5, and especially as explained with respect to the segmental illustration shown in FIGS, 68, the lifter bars 30 and 82, as well as the peripheral liner segment 78, can have the life thereof substantially extended over the present practice where, in mills of this type, lifter bars of substantially the same height now are employed. The relative heights of the longitudinally extending lifter bars 80 and 82 of the mill shown in FIG. 3 can best be appreciated from the sectional view shown in FIG. 4, which is taken on the line 4-4 of FIG. 3. The exemplary thickness of the peripheral liner segments 78, likewise, can be appreciated from FIG. 4.

From the foregoing, it will be seen that the present invention comprises various embodiments of means and an overall method of controlling the wear and the need for replacing both liner members and lifter bars of rotatable tumbling mills of various types. Such means and method are extremely simple and, in addition to minimizing the cost of these elements per se, the present invention also substantially reduces the amount of time required to replace such elements, when actual replacement is required, thereby effecting an overall economy in the operation of the mill, but, more importantly, maintaining a subs-tantially constant contour within the mill, which is especially important with regard to autogenous grinding mills.

The various embodiments of lifter bars and liner segments or sections illustrated and described hereinabove with respect to the mill details shown in FIGS. 1-8 have all been substantially similar. However, it is to be understood that the present invention can be employed with regard to other shapes and types of segmental lining means, as well as lifter bars, certain examples of said additional types and shapes being shown respectively in FIGS. 9-11. In the embodiment shown in FIG. 9, for example, the mill shell 84 supports a plurality of liner segments 86, the opposite edges of which are provided with longitudinal flanges 88 for purposes of adjacent, but slightly spaced, flanges on successive liner segments being received respectively within recesses 90 formed along opposite sides of the lifter bars 92 and 94-. Thus, by securely clamping the liner segments 86 relative to the shell 84, lifter bars 92 and 94 automatically are secured in operative position without requiring bolts or other fastening means to be extended through such lifter bars. As to the present invention, it will be seen that the lifter bars 92 are of the high type, while the intermediate lifter bar 94 is of the medium height type.

A more simple embodiment than that shown in FIG. 9 is shown in FIG. 10, by way of a further embodiment of the present invention, and in which the shell section 96 supports a plurality of circumferentially spaced exemplary liner sections 98, which may be fastened to the shell by any suitable means, such as conventional bolts used for such purpose, but not specifically illustrated in the figure. Within the spaces between successive liner sections 8 are alternately disposed high lifter bars 1% and medium height lifter bars 102. These bars also may be secured to the shell section 96 by appropriate bolts, not shown. All of these liner sections and litter bars are formed from customary types of hard, wear-resistant material, and it will be seen that in the embodiment of FIG. 10, the arrangement of the high and medium height lifter bars alternately between similar liner sections 98 will result in gradual wearing of these elements in the manner described with respect to the phenomenon illustrated in FIGS. 6-8, while maintaining a substantially constant contour within the mill, notwithstanding such gradual wearing of the components comprising the lining and lifting means within the mill.

Still another embodiment is illustrated in segmental and somewhat diagrammatic form in FIG. 11, wherein another shell section MP4 is shown, fragmentarily, while liner segments all of substantially the same Width, but progressively different heights, are employed. Thus, it will be seen that what might be considered the equivalent of liner sections 106 are disposed adjacent shell section 104 and secured thereto by any suitable means, such as customary bolts, not shown, While arranged between spaced liner sections 106 are pairs of relatively broad high lifter bars 108 and medium height lifter bars 110, all of which may be detachably secured to the shell section 104 by suitable bolts, of conventional nature, not shown.

The principal difference between the embodiment shown in FIG. 11 and that shown in FIG. 10, as well as the preceding figures, for example, is that the arrangements in the preceding figures and FIG. 10 is, in successive order, high, low and medium height elements, while in the embodiment of FIG. 11, the successive order is high, medium and low elements. Under certain conditions, particularly in regard to autogenous grinding, it is conceivable that the arrangement shown in FIG. 11 will offer advantages over those shown in the preceding figure-s, particularly for purposes of maintaining optimum grinding conditions of certain types of materials. Accordingly, although a somewhat different successive order of heights of elements is shown in FIG. 11, it, nevertheless, will be seen that there also are somewhat similar, three different heights of elements in all of the other embodiments when the liner segments are considered one of the elements, namely, the elements of lowest height. In View of this, there is a similar basis of invention in the embodiment of FIG. 11 with regard to the embodiment shown in the preceding figures.

Referring to co-pending application Ser. No. 822,612, means and methods of improving the operations of autogenous grinding mills are described and claimed therein, including the principles of making separate tests in a mill using different lining contours. Due to the fact that friable materials differ in their breaking and grinding characteristics when subjected to different impact and comingling actions, a change in the lifting, cascading and mixing actions of various size ranges of one type of material has a very noticeable and definite effect on the overall reduction rate of that material. Another material may act very differently under otherwise similar conditions.

'It is not possible to determine accurately the optimum reduction effect without subjecting a particular material to a test run under different conditions. Changing the lining contour and consequent lifting, cascading and mixing effects during a series of test runs will indicate which contour will accomplish the optimum results. The present invent-ion comprises an important improvement to the means .and methods of said invention described and claimed in said aforementioned application in that once the optimum lining contour is established for a particular material being treated, this contour can for all practical purposes be maintained intact, in the manner described above with reference to the attached drawings.

By making a series of tests in a smaller test mill capable of handling the same size range of material as a large unit, determination can be made of the lining contour suitable to employ in the large unit. This simplifies other- Wise expensive test procedure that would be carried out in a large unit. For example, a 6-foot test mill, capable of handling 8" to 10 feed size, requiring 15 H.=P., can thus be first employed to determine the optimum lining contour. A large mill, 24 feet in diameter, requiring 1500 HP. than can be equipped with the same optimum liner contour with far less time and effort being required than if the testing had occurred in the large mill. Then, by renewing the worn lifter bars in the large mill in accordance with the present invention, such optimum contour of the mill is maintained substantially constant, even though wear progressively occurs within the mill, as described above.

For most autogenous grinding operations, whether a small or large mill is employed, the optimum speed usually ranges between 60% and 85% of the critical and theoretical speed, which is 54.19 {Radius in ft.

regardless of feed size range. While a change in mill speed affects grinding rate characteristics, to make a change of mill speed is usually not easily accomplished, unless a very costly variable speed drive arrangement is employed. Also, the mill with the most effective speed, from the standpoint of grinding efficiency, usually results in a larger, more costly, unit to build and erect. More effective, overall results are accomplished by changing the lining contour and at considerably less overall cost. With the lifter b ar means and method, here described, a still greater advantage is obtained. The contour and grinding efficiency can be maintained relatively constant over an indefinite period of time.

It thus is apparent that the invention covered by said co-pending application, which covers broadly the feature of testing mill operations, and especially autogenous mill operation, to determine the mill contour best suited to achieve optimum efficiency, is even more useful when combined with the present invention which pertains to methods and means of maintaining that optimum contour substantially constant, even though wear progressively occurs within the mill, simply by using alternate lifter bars of different heights and successively replacing such alternate lifter bars, as they become worn beyond further use, with new ones of the greater height.

While the invention has been described and illustrated in its several preferred embodiments, and has included certain details, it should be understood that the invention is not to be limited to the precise details herein illustr ated and described, since the same may be carried out in other Ways falling within the scope of the invention as claimed.

We claim:

1. A method of controlling the wear of the lining surfaces and lifter bars of a tumbling mill to maintain the interior contour of the mill substantially constant over substantial periods of use, said method comprising the steps of utilizing a plurality of lifter bars of at least two different heights extending radially inward from the lining surfaces within the mill arranged alternately in sequence and exposed to the tumbling action of the load within the mill, operating the mill until the lifter bars of lesser height have been worn by impact and abrasion to a degree which renders the lifting capabilities of such bars less effective, and replacing such worn lifter bars of lesser height with new lifter bars of greater height to restore the lifting effect of the interior of the mill to produce substantially the initial sequence of lifting bars and corresponding lifting effect and thereby generally restoring the same interior contour.

2. A method of controlling the wear of the lining surfaces and lifter bars of an autogenous tumbling mill havmg a substantially greater diameter than length to maintain the interior peripheral contour and lifting effect afforded thereby within the mill substantially constant over extended periods of use, said method comprising the step of providing a plurality of groups of lifter bars respec tively of at least two different radial heights extending radially inward from the inner lining surface of the mill and bars of each different height group being arranged relative to the inner lining surfaces of said mill to provide a desired predetermined contour pattern having a desired lifting effect, operating the mill autogen-ously to grind friable material until the lifter bars of original shorter height have been worn by the material to a predetermined extent, and replacing such worn lifter bars of shorter height with new lifter bars of greater height while retaining the partially worn lifter bars originally of greater height, thereby to restore the desired lifting contour pattern to the interior of said mill.

3. The method of maintaining the interior contour of a tumbling mill substantially constant while subjected to wear from abrasion and impact of the material being tumbled therein, said method comprising utilizing lining members interspersed between lifter bars projecting radially inward from said lining members and having different heights and corresponding lifting effects and arranged in a predetermined contour pattern around the interior of the mill resulting in wear upon certain portions of said lining members adjacent bars of one height differently from those ad iacent bars of a different height and, as wear occurs over a period of time, progressively shifting the effective height of said lifter bars circumferentially relative to said lining members to change the wear areas upon said lining members to a different surface portion thereof while substantially maintaining said predetermined contour pattern by substituting maximum lifting effect bars for minimum lifting effect bars when wear upon the lining members at one portion has progressed to a predetermined extent.

4. A method of autogenously grinding friable material comprising a mixture of different size ranges thereof by tumbling within a mill to reduce all of said size ranges of said material to a desired predetermined range of fine sizes comprising the steps of feeding said material to a tumbling mill provided with lifter bars and a lining surface, said lifter bars being of least two different heights and extending radially inward from the lining surfaces of said mill and and arranged alternately in successive relationship relative to the lining surfaces of said mill, observing the grinding results after a predetermined period of time, substituting lifter bars of different heights for those initially used and observing the grinding effect produced by such substituted bars, selecting the alternate lifter bar heights productive of optimum autogenous grinding results, and maintaining said interior contour produced by said selected lifter bars substantially constant by operating the mill until the lifter bars of lesser height are worn by impact and abrasion to a degree which renders the lifting capabilities of such lifter bars less effective, and replacing such worn lifter bars of lesser height with other lifter bars of greater height when needed while continuing to use the partially worn alternate lifter bars.

5. The method according to claim 4 including the further step of removing relatively fine size ranges progressively from said mill by internal screening while the material is being tumbled therein.

6. A rotatable tumbling mill for grinding friable material and comprising in combination, a mill shell; means to support said shell for rotation; lining means connected to the interior of the said shell to protect said shell, and a plurality of lifter bars of at least two different heights extending transversely to the opposite ends of said shell and spaced circumferentially therearound; and means detachably securing said lifter bars to the interior of said mill shell, said bars extending radially inward from said lining means and being arranged relative to said lining means to provide an interior contour of predetermined shape to afford a desired lifting effect upon material when within the mill and being tumbled, said lifter bars of different height being interchangeable with each other and said predetermined interior contour shape being maintained substantially constant by replacing the lifter bars of lesser height which have been worn a predetermined amount with new lifter bars of greater height, whereby the original lifter bars of greater height then are worn substantially to the height of the original bars of lesser height and afford the desired differential in heights of the various lifter bars relative to said lining means.

7. The mill set forth in claim 6 further characterized by said lifter bars of lesser and greater height having lining elements interposed therebetween and said lifter bars each comprising composite lifter means composed of a lower wedge bar engageable with the edges of said lining elements to position the same operatively Within the mill and an upper wear bar portion detachably connected to the upper surface of said lower wedge bar, whereby when an upper wear bar portion is worn a predetermined amount and requires replacement the new wear bar portion is mounted upon the original wedge bar, thus minimizing waste.

8. The mill set forth in claim 6 wherein the mill shell comprises a peripheral portion connecting opposite ends and the lining means and lifter bars of various heights are connected to said peripheral portion of said mill shell and extend transversely relative to the ends of said mill substantially in parallelism with the axis of the mill.

9. The mill set forth in claim 6 wherein the diameter of the mill is substantially greater than the length thereof to render the same suited for effic-ient autogenous grinding.

10. The mill set forth in claim 6 further characterized by said lifter bars of lesser and greater height having lining elements interposed therebetween and said lifter bars each comprising composite lifter means composed of a lower bar portion engageable with the edges of said lining elements to position the same operatively within the mill and an upper wear bar portion detachably connected to the upper surface of said lower bar portion, whereby when an upper wear bar portion is worn a predetermined amount and requires replacement the new wear bar portion is mounted upon the original lower bar portion, thus minimizing waste.

11. The mill set forth in claim 6 further characterized by said predetermined shape of interior contour of the mill shell in the direction of rotation of the mill comprising lifter bars of greater and lesser height and lining members being between all successive lifter bars.

12.. The mill set forth in claim 6 further characterized by said predetermined shape of interior contour of the mill shell in the direction of rotation of the mill comprising lifter bars of greater and lesser height adjacent each other and preceding a lining member.

References Cited by the Examiner UNITED STATES PATENTS 1,207,174 12/16 Johnson 241183 20 2,949,247 8/60 Rosengvist et al 241183 3,078,050 2/63 Hardinge 241-70 XR FOREIGN PATENTS 7801 1911 Great Britain.

25 J. SPENCER OVERHOLSER, Primary Examiner. 

1. A METHOD OF CONTROLLING THE WEAR OF THE LINING SURFACES AND LIFTER BARS OF A TERMINATING MAIL TO MAINTAIN THE INTERIOR CONTOUR OF THE MILL SUBSTANTIALLY CONSTANT OVER SUBSTANTIAL PERIODS S OF USE, SAID METHOD COMPRISING THE STEPS OF UTILIZING A PLURALITY OF LIFTER BARS OF AT LEAST TWO DIFFERENT HEIGHTS EXTENDING RADIALLY INWARD FROM THE LINING SURFACES WITHIN THE MILL ARRANGED ALTERNATELY IN SEQUENCE AND EXPOSED TO THE TUMBLING ACTION OF THE LOAD WITHIN THE MILL, OPERATING THE MILL UNTIL THE LIFTER BARS OF LESSER HEIGHT HAVE BEEN WORN BY IMPACT AND ABRASIVE TO DECREE WHICH RENDERS THE LIFTING CAPABILITIES OF SUCH BARS LESS EFFECTIVE, AND REPLACING SUCH WORN LIFTER BARS LESS EFFETIVE, NEW LIFTER BARS OF GREATER HEIGHT TO RESTORE THE LIGTING EFFECT OF THE INTERIOR OF THE MILL TO PRODUCE SUBSTANTIALLY THE INITIAL SEQUENCE OF LIFTING BARS AND CORRESPONDING LIFTING EFFECT AND THEREBY GENERALLY RESTORING THE SAME INTERIOR CONTOUR.
 6. A ROTATABLE TUMBLING MILL FOR GUIDING FRIABLE MATERIAL AND COMPRISING IN COMBINATION, A MILL SHELL; MEANS TO SUPPORT SAID SHELL FOR ROTATION; LINING MEANS CONNECTED TO THE INTERIOR OF THE SAID SHELL TO PROTECT SAID SHELL, AND A PLURALITY OF LIFTER BARS OF SAID LEST TWO DIFFERENT HEIGHTS EXTENDING TRANSVERSEY TO THE OPPOSITE ENDS OF SAID SHELL AND SPACED CIRCUMFERENTIALLY THEREAROUND; AND MEANS DETACHABLY SECURING SAID LIFTER BARS TO THE INTERIOR OF SAID MILL SHELL, SAID BARS EXTENDING RADIALLY INWARD FROM SAID LINING MEANS TO PROVIDE AN INTERIOR CONTOUR OF PREDETERMINED MEANS TO PROVIDE AN INTERIOR CONTOUR OF PREDETERMINED SHAPE TO AFFORD A DESIRED LIFTING EFFECT UPON MATERIAL WHEN WITHIN THE MILL AND BEING TRUMBLED, SAID LIFTER HARS OF DIFFERENT HEIGHT BEING INTERCHANGEABLE WITH EACH OTHER AND SAID PREDETERMINED TUBULAR CONTOUR SHAPE BEING MAINTAINED SUBSTANTIALLY CONSTANT BY REPLACING THELIFTER BARS OF LESSER HEIGHT WHICH HAVE BEEN WORN A PREDETERMINED AMOUNT WITH NEW LIFTER BARS OF GREATER HEIGHT, WHEREBY THE ORIGINAL LIFTER BARS OF GREATER HEIGHT THAN ARE WORN SUBSTANTIALLY TO THE HEIGHT OF THE ORIGINAL BARS OF LESSER HEIGHT AND AFFORD THE DESIRED DIFFERENTIAL IN HEIGHTS OF THE VARIOUS LIFTER BARS RELATIVE TO SAID LINING MEANS. 